'The Big Bang Theory' Season 9 spoilers: Sheldon, Amy to get closer; what's in store for the couple?

Sheldon will trust Amy with a secret in "The Solder Excursion Diversion."

Amy and Sheldon's relationship is getting stronger and this week's episode of "The Big Bang Theory" will see him trusting his girlfriend with one of his best kept secrets.

Thursday's episode is titled "The Solder Excursion Diversion" and according to the summary on CBS, Amy and Sheldon will go shopping for a laptop, and she will be shocked at a revelation from her boyfriend.

"They explicitly talk about that this is a new level of trust, and that's really special," Mayim Bialik, who plays Amy, told Entertainment Weekly, adding that it's a really sweet episode.

While the secret isn't a monumental one, actor Jim Parsons noted that it helps to advance Amy and Sheldon's relationship as a couple. "The [writers] are doing one thing after another to keep that relationship advancing without shoving it into the future," Parsons told Entertainment Weekly. "This is one of those things that doesn't necessarily change anything from a viewers' perspective on a day-to-day basis of watching the show, but in a subconscious way and from the groundwork of the show in general, it adds a layer of something between them."

Although the actors did not say what the secret is, a leaked description of the episode on Wikia revealed that Amy will find out about Sheldon's hoarding habit. When Amy suggests that Sheldon throw away his damaged laptop, he will reveal that he has a storage unit where he keeps all the stuff that he can't throw away. Apparently, Sheldon also makes Amy sign a non disclosure agreement after revealing this secret.

Elsewhere in the episode, we'll see Raj sells out Leonard and Wolowitz after they lie to Penny and Bernadette to attend an early screening of a movie.